Electrical vacuum pump



May 12,1942. c., w. HANSELL ELECTRICAL VACUUM PUMP Original Filed Jan. 6, 1938 2 Sheets-Sheet l 0 MQ O-MGJMMWM Z AMPERES IN FIELD COIL ACINPUT INVENTOR. K HANSELL I I ATTORNEY. H

INVENTOR. HAM/SELL A TTORN 2 Sheets-Sheet 2 1 Filed Jan. '6, 1938 C. W. HANSELL ELECTRICAL VACUUM PUMP Origina May 12, 1942.

RECTIFIER ACPOWER INPUT Patented May 12, 1942 2,282,401 a UNITED STATES PATENT'OFFICE ELECTRICAL VACUUM PUMP Clarence W. Hansell, Port Jefferson, N. Y., assignor to Radio Corporation of America, a. corporation of Delaware Application January 6, 1938, Serial No. 183,584 Renewed January 30, 1940 19 Claims. (Cl. 230-69) This invention relates to a new and novel imof an electron has been determined to be about proved electrical vacuum pump and is a further sixty-five centimeters, or twenty-five inches. I improvement in the electrical vacuum pump of have also found that by placing a metallic shield the type described in my United States Patent having a central hole and locating the shield 2.022465, granted Nov. 26, 1935. between the cathode and anode and applying a An object of this invention is to further immagnetic field with fiux lines parallel to the axis prove electrical vacuum pumps by the addition of of the pump or tube, those electrons which leave a magnetic field which is so arranged in con the cathode in undesired directions, away from junction with the vacuum pump that the elec-- the axis, may be made to return to the vicinity tron paths are brought closer together and l: lengthened out, which results in increasing the paths P s g thrOugh the e n e S ield- In Speed of the pumping action and increasing the practice, the shield may be connected to, or form final obtainable vacuum. a part of the anode in which case after enter- A feature of this invention resides in the aring the anode, the electrons continue to follow rangement of an electron discharge tube within helical paths until they get to a region of dea field coil so that a magnetic field is established creased magnetic field which then allows them through the tube with the lines of magnetic force to land upon the surface of the anode. substantially parallel to the axis of the tube. This invention will best be understood by re- Another feature of this invention is the focusferring to the accompanying drawings, in which: ing of the electron stream within the electron :0 Fig. 1 is a curve showing some experimentally discharge tube, resulting in a further increase determined characteristics indicating an increase in the pumping action, as will be explained more in current flowing between an anode and cathode fully ter, of a tube when the tube was placed in the pres- I have found that, by the use of a magnetic ence of a variable magnetic field which increased field through a rather long electron discharge the length of electron paths.

tube, the length of electron paths between the Fig. 2 is a simple form of this invention. filament and anode can be increased. The in- Fig. 3 is another embodiment of this invencrease in electron paths length is obtained betion; and

cause the magnetic field tends to restrict the Fig. 4 is a still further improvement of the paths to make them more nearly parallel to the embodiment shown in Figs. 2 and 3.

axis of the tube so that electrons can, on the 1 Referring now in detail to the drawings, it will average, travel a much greater distance along the be noted that in the curves shown in Fig. 1, as tube before striking the tube wall. Electrons northe current is increased in the field coil there is mally tend to take paths spreading out more or produced a corresponding increase in magnetic less in all directions from the source so that the 3 field, the electron current increases as a result of electron motions have components at right angles increased ionization" which lowers the space to the axis of the tubes. Addition of the mag charge voltage drop and increases the cathode netic field tends to cause deflecting or bending emission. of the motions at right angles to the axis, making Fig. 2 shows one form of electrical vacuum the electrons follow helical paths parallel to the pump which makes use of a magnetic field. It xi consists of a cathode l and an anode 2, both of The application of a. magnetic field gives many Which are so arranged that when electron ourof the electrons a longer spiraled path and thererent flows between them in the presence of gas, fore the probability for collision with gas molethe gas will be ionized and move toward the oathcules is greatly increased. This causes an inode in a manner to pump the gas out of a chamcrease in ionization with a resultant increased her to be evacuated. The anode consists preferpumping efiect for a given value of cathode elecably of a metal tube, which is closed at one end tron emission current. At the same time, the by a metallic shield 3 having a small aperture 4 final obtainable degree of vacuum for a given of moderate dimensions, for example, 0.01 to 0.5 current, is increased because of the increased centimeter diameter, depending upon the availratio of mean electron path to mean electron able electron emission current from the cathode. free path in the gas. Each electron, since it can Surrounding anode 2 and shield 3 is a magnetic travel over a longer path, has a greater probafield coil 5 which is electrically connected to a bility of collision with a molecule. For example, direct current input source 6. A field rheostat 1 at one micron pressure in air, the mean free path is connected in series between the direct current current and strength of the magnetic input and the field coil 5 to vary the magnetizing field. At tubular anode, there is located a glass envelope 8 to which the metallic anode is sealed at a point adjacent the field coil 5. Cathode is supported substantially centrally with respect to the axis of the field coil and faces aperture 4. Cathode is heated by an alternating current input source in the form of a transformer 9, the center point of the secondary of which is connected to the minus side of the direct current input 6, the positive side of the direct current input being connected to anode 2. The far end of the tube forming the anode is tapered at a point ID to receive the outlet from the object II to be pumped or evacuated. The lower portion |2 of envelope 8 is arranged for connection to an outlet which makes fluid connection with rough vacuum pump l3.

In the modification shown in Fig. 3, a hot cathode or heavy filament I5 is mounted symmetrically with respect to the axis of an anode l6 which is in the form of along thin metallic tube. Interposed between cathode l5 and anode I6 is a metallic diaphragm or ring-like member I! having an aperture l8. Directly behind cathode IE is arranged a negatively charged shield l9 which with aid of a magnetic field, tends to focus the electron emission of the cathode upon the aperture I8. The cathode, which is preferably in the form of a ring around the axis of the hole in the diaphragm, gives a cone-like path of electron emission focused upon the aperture, and this emission tends to diverge after passing through the aperture, as is indicated by the broken lines 20. However, when an axial magnetic field is applied, by passing current through the field coil 2|, which aids the focusing action and limits the divergence of the electron emission after it is passed through the aperture l8, due to the magnetic field and the initial radial component of velocity, each electron is made to follow a helical path after passing the anode diaphragm. This helical path of each electron tends to pass through the axis of the system at frequency intervals and the total length of the path may be many times greater than would be obtained without the application of the magnetic field. The electron paths all tend to come together at the same points where each path passes through the axis of the tube. Although there is shown only one diaphragm, it is possible to place additional diaphragms with holes through their centers at each electron focusing point in order to increase the pumping action. Other structural members of this improved electrical vacuum pump comprise envelope 22 having a stem 23 for connection to 'rough pump I3, and a stem or press 24 for supporting shield |9 and filament l5, filament l5 being heatedfrom an alternating current power source 25, which is and rectifier 26. The secondary central connection of transformer 3 is connected to shield l9 through a resistance 21, also, a variable negative potential is applied to shield H! by means of a variable resistance 28. The positive side of the rectifier is connected directly to anode I6 and one side of the winding of field coil 2|, the negative side of the rectifier being connected in series with a variable resistance 29.

A preferred embodiment of this invention is shown in Fig. 4, which consists of a field coil 30 surrounding a long insulating tube 3| which is electrically connected to and extends from a first one end of the through the hole in connected to transformer 9 diaphragm anode 32 to a second anode 33 which is maintained at a much higher. direct current potential than anode 32. Insulating tube 3| is lined with a very thin layer of high resistance conducting material 34, which is similar to material employed in some of the so-called metallized resistors." Due to the high resistance conducting material 34, a substantially uniform electric field is maintained within the long tube 3|. This field tends to lengthen the electron paths 35 and increas the electron velocities. In addition, it also causes all ions formed by collision of the electrons and molecules to move toward the oathode. There is a further advantage in employing the long tube with a potential gradient throughout its length, in that secondary electrons produced by collision of primary electrons and molecules of gas with the conducting material lining the tube are accelerated toward anode 33 and are caused to add to the production of the ionization of any gas in the tube. To reduce the bombardment of the cathode and protect it from the effect of occasional arcs, there are provided resistance elements 36 and 31 through which emission current from the cathode must pass. These resistances should be high enough to limit the cathode emission current to safe values or to values below the available electron emission from the cathode l5. In addition to the detail shape and arrangement of the cathode, a shield l9 and and first anode orifice 38 are provided to reduce the tendency for ions to strike the cathode and to make them strike the shield instead. This shield is made with substantial mass and heat radiation to withstand bombardment.

However, in order to more fully protect the tube and circuit, the resistance 36 is connected in series with the shield and the negative side of the rectifier unit 26, so that a limited amount of current can flow through it. However, resistance 36 should be considerably smaller in value than resistor 31, which is connected in the cathode circuit. The envelope 40 is arranged on the metal anode structure 32 in such a manner that this portion of the pump on which the cathode and shield are held may be interchangeable, so as to furnish new elements as required, by providing a flange 4|, metallic band clamp 42, and gasketed joint 43, which may be in the form of a mercury seal, a low melting point fusable alloy seal such as for example woods metal, or the like. Such an arrangement greatly facilitates cathode renewals, particularly since the joints are really a part of the rough pump system, rather than the high vacuum system.

In the operation of this invention, a fair degree of vacuum is maintained in the system by means of rough pump l3. The cathode is then heated up to a temperature which causes electrons to be emitted and then the direct current potential is applied to the anode elements and the magnetic field is built up to a value in which the electron paths are suitably lengthened focused to give the maximum pumping effect. When the pump is started, the initial stage of pumping may be shortened by connecting some or all of the elements of the tube to be exhausted to a source of high positive direct current potential or direct current and alternating current superimposed which is high enough to cause a direct current discharge from the elements of the tube to the electrodes of the .pump. Naturally, the tube to be exhausted should be heated during evacuation in the usual manner. A pump of the type described has many advantages not interposed between possessed by other types of vacuum pumps, such as the Langmuir vapor jet-condensation pump, which requires low temperature traps to keep vapors out of the vessel which is to be exhausted.

Although only a few embodiments of this invention have been shown, it is to be distinctly understood that it should not be limited to the arrangement illustrated.

What is claimed is:

1. Vacuum producing apparatus comprising in combination an electron discharge device having an inlet associated with an object to be evacuated, an outlet, a cathode located at one end of said electron discharge device, a metallic anode adjacent said cathode, a second anode spaced magnetic field for increasing the length of the electron path in said electron discharge device.

2. Vacuum producing apparatus comprising in combination an electron discharge device havapart from said first anode by an insulating tube, means for supplying a voltage substantially higher to said second anode than to said and magnetic anodes for producing a magnetic field for increasing the length oi the electron path in said electron discharge device.

3. Vacuum producing apparatus comprising in combination an electron discharge device having said insulating tube, means for supplying a voltage substantially highthan to said first anode, interposed between said anodes for producing a magnetic field for increasing the length of the electron path in said electron discharge device.

4. Vacuum producing apparatus comprising in combination an electron discharge device having an inlet associated with an object to be evacuated, an outlet, a cathode located at one end oi said electron discharge device, a metallic anode adiacent said cathode, a removable support member for said cathode, a second anode spaced apart from said first anode, means for supplying and magnetic means a voltage substantially higher to said second an-- ode than to said first anode, and magnetic means said anodes for producing a magnetic field for increasing the length or the electron path in said electron discharge device.

5. Vacuum producing apparatus comprising in combination an electron discharge device .having an inlet associated with an object to be evacuated, an outlet, a cathode located at one end of said electron discharge device, a metallic anode adjacent said cathode, a second anode spaced apart from said first anode by an insulating tube. means adjacent said first mentioned anode for removing said cathode, means for supplying a voltage substantially higher to said second anode than to said first anode, and magnetic means interposed between said anodes for producing a i length 01 the magnetic field for some;

electron path in said electron discharge device.

rear of said cathode, a metallic anode adjacent said cathode, asecond anode spaced apart from said first anode, means for ode spaced apartfrom said first anode, a central aperture in both of said anodes, means adjacent said cathode, a second anode spaced apart from said first anode, a magnetic field coil located between both of said anodes, an alternating current supply source connected to said cathode, a rectifier connected the current therethrough, and the magnetic fiux in said field electron path means for varying coil to increase the in said electron discharge device.

9. An electron vacuum pump comprising an electron discharge device having an inlet associated with the object let, a cathode located at one end of said device, a shield in the rear of said cathode, an anode located adjacent said cathode, said anode having a portion 01. reduced diameter at the end away from said cathode, a metallic diaphragm having an aperture within said device, said diaphragm being located intermediate said cathode and said anode, and means between said inlet and said outlet for producing a magnetic field to lengthen the electron path between said cathode and said anode;

said device, and a magnetic field coil surrounding said anode for producing a magnetic field to lengthen the electron path between said cathode and said anode.

11. An electron vacuum pump comprising an electron discharge device having an inlet associated with the object to be evacuated, and an outlet, a cathode located at one end oi. said device, an anode in the form 0! a long metallic tube .3 the length of the to be evacuated, and an outlocated at the other end of said device, and means surrounding said anode for producing a magnetic field to lengthen the electron path between I said cathode'and said anode.

12. An electrical vacuum pump comprising an electron discharge device having an inlet associated with the object to be evacuated, and an outlet, an insulating tube, a cathode centrally located at one end of said device, an anode located at each end of said insulating tube, a removable support member for said cathode, and means surrounding said insulating tube for producing a magnetic field to lengthen the electron path between said cathode and at least one of said anodes.

13. Vacuum producing apparatus comprising in combination an electron discharge device having an inlet associated with the device to be evacuated, and an outlet, an anode and a cathode, a magnetic field coil surrounding the anode of said electron discharge device, an alternating current input supply source connected to said cathode, a direct current source connected to said anode and a midpoint of potential on said cathode and one side of said field coil, and variable means connected to the other sideoi said field coil and to said direct current source for varying the magnetic flux in the coil surrounding said anode.

14. Vacuum producing apparatus comprising in combination an electron discharge device having an inlet associated with the device to be evacuated, and an outlet, an anode and a cathode, a magnetic field coil located between said anode and said cathode, an alternating current supply source connected to said cathode, a rectifier having its input connected to said alternating current source and its output connected to said field coil for supplying direct current thereto, a variable resistance connected in series with one side of said rectifier and said field coil for varying the current thereto, and a connection between saidfield coil and a point of mid-potential and said cathode.

15. An electron vacuum pump comprising an electron discharge device having an inlet associated with the device to be evacuated, and an outlet, at least an anode and a cathode, said cathode located at one end of said device, said anode located at the other end of said device, means adjacent said anode for producing a magnetic field to lengthen the electron path with the said anode, a mechanical pump, and means including a first and a second aperture in said device ior fluid communication with said electron discharge device and said mechanical pump.

16. An electrical pump comprising an electron discharge device having an inlet associated with the device to be evacuated, and an outlet, a cathode located at one end of said device, a long tubelike anode, a metallic shield having an aperture therein and located within said tube-like anode, means for passing electrons through the aperture in said shield in one direction and ions and molecules of gas through the aperture of said shield in the opposite direction, and a magnetic field surrounding said tube-like anode for increasing the efllciency of said pump.

17. An electrical vacuum pump comprising an electron discharge device having an'inlet associated with the device to be evacuated, and an outlet, a cathode located at one end of said electron discharge device, an anode intermediate said inlet and said outlet, a shield located intermediate said cathode and said anode, and means located between said inlet and said shield for producing a magnetic field to increase the pumping speed of said device. f

18. An electrical vacuum pump comprising an electron discharge device having an inlet associated with the device to be evacuated, and an outlet, a cathode located at one end of-said electron discharge device, an anode intermediate said inlet and said outlet, a shield located intermediate said cathode and said anode, a tube which is relatively long with respect to its width located between said inlet and outlet, and means surrounding said tube for producing a magnetic field to increase the pumping speed of said device.

19. An electrical pump comprising an electron discharge device having an inlet associated with an object to be evacuated, and an outlet, a cathode located at one end of said device, an anode intermediate said inlet and said outlet, a magnetic disc serving as a shield and located intermediate said cathode and said anode, means ineluding an aperture located in said shield for passing electrons therethrough in one direction and ions and molecules of gas through the aperture in the opposite direction, and a magnetic field adjacent said anode for increasing the emciency of said pump.

CLARENCE W. HANSELL. 

